The invention relates to a refrigeration system for cooling the interior of a mobile cooling chamber, for example of a container which can be used universally, for example, on ships, or of a truck, a small transporter, or a cooling wagon, said refrigeration system being part of a cooling chain for transporting cooled and frozen products. The invention therefore relates to a refrigeration system for cooled transportation. For said cooling chambers, the terms container interior, container or cooling container are used in the text below. Accordingly, the term container cooling system is used to represent said mobile cooling chambers to be cooled.
The conducting of cooling air and basic construction of cooling containers for ships are described in DE 202007008764. The interior of a cooling container is surrounded by thermally insulated side walls, a roof and base, wherein the inner base is generally also designed with air distribution devices, for example longitudinal ribs, which form passages for the conduction of cold air.
Cooling containers also have to be constructed in such a manner that they can be transported by road, sea or rail by the relevant transportation systems in each case (truck-trailer reefers, marine reefers or rail reefers).
In this case, the usable temperature of such a container interior is dependent on the cargo to be cooled. Such cooling containers have to be capable of carrying out cargo cooling or freezing processes and then of keeping the cargo at a predetermined level, the cooling storage temperature.
The refrigerating capacity during the cooling or freezing process and during cooling transportation storage differs very significantly for the same container size depending on the product properties and usable temperature level in the container interior.
During the cooling transportation of a container, different climatic ambient conditions generally prevail at the outer wall of the container, said ambient conditions being caused regionally by passing through different climate zones or simply by the diurnal variation in the temperature, and therefore the temperature level of the heat sink changes and thus so does the condensation temperature of the refrigeration system for the container cooling system.
As a result, it has to be possible for the refrigeration system for the container cooling system to be operated efficiently and to be variable in such a manner that the refrigerating capacity and usable temperature can be varied and operation can be carried out economically and in an environmentally friendly manner at the different condensation temperatures without any restrictions.
The cooling container with its refrigeration system has to be operable in a container stack and the operating regime thereof has to be adaptable individually to the transported product to be cooled.
In addition, the amount of space required by, and mass of, a mobile refrigeration system should be as small as possible.
In refrigeration systems for the container cooling system use is made, according to the prior art, of single-stage or two-stage refrigeration systems which have compressors, condensers, expansion devices and evaporators.
The container is directly cooled by circulating refrigerant by means of which heat from the chamber to be cooled is absorbed at the evaporator. For this purpose, the refrigerant is compressed in one or more stages, in one or more compressors, to a higher pressure and therefore to a condensation temperature above the heat sink (container surroundings) and is then cooled in a gas cooler or in a condenser by dispensing heat to the surroundings and is then expanded again in one or more stages to the pressure in the evaporator, thus producing liquid refrigerant and flash vapor at the lower evaporation temperature of the refrigerant. This arrangement is embodied in each case only in a single stage or only in multiple stages, and therefore said refrigeration system is not suitable, either in the single-stage embodiment, or in the two-stage embodiment for the desired breadth of use of a cooling container.
U.S. Pat. No. 4,730,464 describes a cooling system for cooling a chamber with air, comprising a compressor and a turbocharger. However, the variability of the refrigeration system is extremely limited in respect of refrigerating capacity and evaporation temperature.
DE 3620847 discloses an absorption refrigeration system which is supplemented by a heat exchanger tube solar collector. The lack of possibility of being able to stack such a cooling container is disadvantageous for use on ships.
Container cooling systems with storage action but without dedicated refrigeration, with what is referred to as indirect cooling, are also known. In this case, the refrigerating medium is cooled away from the container and is subsequently introduced into cavities on the container. According to DE 29722052, slurry ice, also referred to as binary ice, cools the wall of the container. In this case, the cooling temperature is defined by the ice, which consists of water and additives, and therefore is not very variable. The cooling of an individual container at a different temperature is not possible, and the cooling duration is limited.
In addition, ice and liquid are not distributed homogeneously in the generally vertical walls.
DE 9110982U1 discloses a container cooling system and the passage system, which is required for this purpose, using cooled water which is provided by a cold water production system without heat exchangers on the cooling container coming into contact with fluorinated hydrocarbons. The container, disadvantageously, cannot be used independently.
By using water as the refrigerating medium, the use of this patent is directed towards the transportation of products above freezing point. This also restricts the use of the cooling container.
In EP0664426, the wall of the container is provided with tubular heat exchanger surfaces through which a heat exchanger fluid is conducted with a phase change. The cooling process is very sluggish, and therefore it is not possible to achieve cooling in a manner suitable for the requirements.